This invention relates to structure for confining an electric arc and, more particularly, relates to arc-extinguishing structure such as an arc chute for an electric circuit breaker.
Most electric circuit breakers contain a pair of normally-closed separable arcing contacts through which current flows just prior to opening of the circuit breaker. When circuit interruption is to be effected, these contacts are separated, and an electric arc is initiated between them. Circuit interruption is normally accomplished by extinguishing this arc within a short time after its initiation. One way of accomplishing this is to utilize an arc chute for elongated and/or dividing the arc and for cooling the hot arcing products, thereby deionizing the gap between the contacts so as to prevent the arc from reigniting after a natural current zero, assuming an a.c. circuit.
In one type of arc chute we are concerned with, there are a pair of spaced-apart side walls of electric insulating material for laterally confining the arc and the arcing products and a plurality of spaced-apart metal plates extending transversely of the arc and having edges against which the arc is driven to effect division of the arc and further cooling of the arcing products. These sidewalls have typically been made of an insulating material that is the heat and pressure reacted thermoset product of several constituents, one of which is chrysotile asbestos, used in relatively large percentages of the total weight of the material.
The use of chrysotile asbestos in such insulating material is advantageous in that it imparts to the material good impact strength, good tensile strength, and fair-to-good arc-erosion resistance. But a significant disadvantage of using chrysotile asbestos as a component of the material is the possible health problem associated with the handling of chrysotile asbestos during manufacture of the material.